Ruthenium-Catalyzed Oxidative Annulation and Hydroarylation of Chromene-3-carboxamides with Alkynes via Double C–H Functionalization

Ruthenium-catalyzed oxidative annulation
of 2H-chromene-3-carboxamides with alkynes has been
achieved by using
the directing group nature of amide in the presence of Cu­(OAc)2·H2O as an oxidant and AgNTf2 as
an additive. This reaction offers a broad substrate scope, and both
symmetrical and unsymmetrical alkynes can be harnessed. High regioselectivity
was achieved in the case of unsymmetrical alkynes. In addition, we
have also accomplished double C–H activation by employing an
excess of alkyne, where both annulation and hydroarylation took place
regio- and stereoselectively in one pot, with the catalyst playing
a dual role. While the first C–H functionalization could involve
Ru–N covalent bond, the second C–H functionalization
most likely involves Ru–O coordinate bond. The structures of
key products are confirmed by X-ray crystallography.